A wide variety of automated chemical analyzers are known in the art and are continually being improved to increase analytical menu and throughput, to reduce turnaround time, and to decrease requisite sample volumes. These analyzers conduct assays using reagents to identify analytes in biological fluid samples such as urine, blood serum, plasma, cerebrospinal liquids and the like. For convenience and safety reasons, these fluid samples almost universally contained in capped sample tubes. The assay reactions generate various signals that can be manipulated to determine the concentration of analyte in the sample. See for example, U.S. Pat. Nos. 7,101,715 and 5,985,672 and assigned to the assignee of the present application and incorporated herein by reference. Improvements in analyzer technology, however, may be hampered if sufficient corresponding advances are not made in pre-analytical sample preparation and handling operations like sorting, batch preparation, centrifugation of sample tubes to separate sample constituents, cap removal to facilitate fluid access, and the like.
To address this need, commercial automated pre-analytical sample preparation systems, called Laboratory Automation Systems (LAS), have been developed to automatically transport sample in tubes to a number of pre-analytical sample processing stations that have been “linked together” like described in U.S. Pat. Nos. 6,984,527 and 6,442,440, both incorporated herein by reference. These LAS handle a number of different patient specimens contained in standard, bar code-labeled, evacuated tubes. The bar code label contains an accession number coupled to demographic information that is entered into a hospital's Laboratory Information System (LIS) along with test orders and other desired information. An operator places the labeled tubes onto the LAS system which automatically sorts and routes samples to the requisite processing devices for pre-analytical operations like centrifugation, decapping, and aliquot preparation prior to the sample being subjected to analysis by one or more analytical stations also “linked” to the LAS.
For certain clinical assays, plasma, obtained from whole blood by centrifugation, is used in the analysis. To prevent clotting, an anticoagulant such as citrate or heparin is added to the blood specimen immediately after it is originally obtained or the anticoagulant is placed in an empty blood collection tube prior to the patient sample being obtained. The specimen may then be centrifuged at a later time to separate plasma from blood cells.
For some biochemical laboratory tests, plasma and blood serum can be used interchangeably. Serum resembles plasma in composition but lacks the coagulation factors as serum is obtained by allowing a blood specimen to clot prior to centrifugation. For this purpose, a serum-separating tube may be used which contains an inert catalyst (glass beads or powder) to facilitate clotting as well as a portion of gel with a density designed to take up a location between the liquid and cellular layers in the tube after centrifugation, making separation more convenient. However, the anticoagulants in plasma can interfere with certain analytical results on serum.
Coagulation tests diagnosis hemorrhagic conditions such as hemophilia, where one or more of the twelve blood clotting factors may be defective, require all clotting factors to be preserved. A citrated evacuated blood collection tube is usually used, as the anticoagulant effects of citrate is dependent upon concentration and can be reversed for testing. Serum, therefore, is therefore inappropriate for coagulation tests.
From the above, it can be seen that analytical tests may be performed on whole blood, plasma or serum, and that sometimes either plasma or serum may be used. Thus, different centrifugation processes may be required for different patient samples depending upon which clinical tests are to be performed by which analytical stations. Differential spin rates and lengths of time are examples of variables that make up what are hereinafter termed “centrifuge protocols” for different samples. For purposes of processing efficiency, when incoming samples are placed into an LAS, it is a general practice to set aside and “batch-together” those samples that have the same centrifuge protocol requirement. At a convenient time, an available centrifuge is adjusted to operate with the operating parameters to provide the required centrifuge protocol and the batch of samples are processed as a group.
In general, centrifugation requires tens of minutes for cycling through a load of tubes by loading centrifuge baskets in a balanced pattern with blood samples taken from the LAS conveyor, spinning the loaded centrifuge baskets, unloading the processed tubes and returning them to the LAS conveyor. If all samples to be handled by an LAS are of routine priority, samples are processed in a first-in-first-out scheduling process. However, non-routine samples requiring a shortest possible turn-around-time (STAT) arise in emergency and surgical operations. STAT samples are consequently given the highest possible priority so as to require the shortest time between receipt and analytical result. STAT samples are identified during loading onto the LAS, are routed ahead of routine samples and are centrifuged per the requisite centrifuge protocol prior to being shuttled to an appropriate analyzer. An undesirable and unavoidable delay arises when the LAS centrifuge is set up for one centrifuging protocol and the STAT sample has a different centrifuging requirement; this requires that centrifugation of samples in the centrifuge be completed and unloaded and that the established protocol be changed to match the STAT sample's requirements. As disclosed in U.S. Ser. No. 11/448,287 incorporated herein by reference, this delay can be partially ameliorated by providing more than one centrifuge set up with different operating protocols. While this provides flexibility if different centrifuges are operated with different operating protocols, throughput may be adversely affected unless the incoming operating load or demand is balanced to match centrifuging capacities. In addition, for simplicity in managing the incoming stream of samples to be centrifuged, incoming samples are processed in the order in which they are introduced to the LAS with different centrifuges being evenly “fed” with samples to be processed. STAT samples are simply placed at the front of the line of incoming samples.
To resolve the difficulties associated with handling samples that require different centrifuge protocols and simultaneously providing accelerated pre-processing for high-priority STAT samples, an LAS having two centrifuges will batch together those samples having the same centrifuge requirements and send them alternately to the two centrifuges. When a STAT sample appears, it is transported to whichever of the two centrifuges can be unloaded must quickly and then the STAT sample is processed immediately if the centrifuge's operating conditions match the STAT sample's centrifuging protocol. If not, the centrifuge's operating conditions must be changed to match the STAT sample's centrifuging protocol and then the STAT sample may be properly centrifuged and conveyed to an appropriate analyzer.
U.S. Pat. No. 6,060,022 discloses a LAS that is operated as generally described above. The LAS has an input workstation, one or more analyzers, and an automated centrifuge for automatically processing multiple sample containers. The workstation includes multiple input locations for inputting sample containers with at least one location selected for high-priority samples. Only one centrifuge is employed, thereby introducing processing inefficiencies because of the relatively long time required for centrifuging. As discussed above, samples having similar centrifugation requirements are “staged together” and processed in serial batches until all are completed. STAT samples are placed at the front of the line of incoming samples but are not given any special priority as far as being centrifuge processing within a batch.
Although LAS have advanced the art of sample handling and processing, there remains the challenge of enabling STAT samples to be presented to a centrifuge processing station from the conveyor of an LAS in a scheduling order that minimizes delays from other samples scheduled to be processed by the same centrifuge. Because of the life-saving implications of even slightly reducing the time from receipt of an STAT sample until that STAT sample is made available to a clinical analyzer, such an improvement is highly desirable.